The Q&A Archives: Brown rubber mulch

Question: I bought Preen weed preventer and put it around the tree in my front yard, then I bought brown rubber mulch and put it around the tree. Now I have yellow dry substance on top of the brown rubber mulch which disappears when I put water on it but comes back and turns yellow again. Any suggestion on what this is and how to stop it. Thanks

Answer: It sounds like a stain from the Preen and I suspect it will wear off and disappear on its own eventually. Preen works to prevent weeds seeds from germinating by releasing a gas of sorts. The chemicals in Preen volitalize and evaporate into the air and what you are seeing is probably a residue from that action. At this point about all you can do is allow it to weather away on its own. If the rubber mulch is thick enough, you won't need to reapply a pre emergent product to keep weeds from sprouting. The thickness of the mulch should be sufficient to keep weed seeds from germinating. Best wishes with your landscape.

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